France, the European Union's largest producer, is widely expected gather a larger wheat crop this year but grain quality, as measured by criteria including protein content, is also crucial to secure sales to foreign milling customers.

"We have begun the wheat harvest on the Atlantic coast, with good to very good yields and some weakness in protein which at the moment is around 10.7-10.8pc," Francois Berson, head of grain procurement, said in a video on Soufflet's Twitter account.

"So it's a little below the minimum 11pc objective for export."

Traders have said the relatively low protein readings, an effect of very strong yields, have led to cheaper animal-feed wheat prices being quoted at the west coast port of La Pallice, predominantly a milling wheat export zone.

Soufflet's Berson said it was too early to give indications about the new wheat crop in the rest of France, with significant harvest progress not expected in other regions before Thursday.

Family-owned Soufflet is one of France's largest grain handlers and exporters.

For winter barley, harvesting of which is already well advanced across France, Soufflet was also seeing some weakness in protein along with varied yields, Berson said.

The west coast was showing "exceptional" yields that were 1.5-2 tonnes per hectare higher than normal, while elsewhere yields were satisfactory but more mixed, he said.

Quality was good except for protein levels that were averaging at 10pc for over 400,000 tonnes of winter barley collected by Soufflet so far, he said, adding that protein remained above a 9.5pc minimum to meet market specifications.